Hi
This happens all the time for me in several computers:
It goes away after a while, the problem is it can’t index My Pictures, My Music, My Videos at some point, but those don’t really exist or are moved after boot, not really sure but it’s really annoying.
Also the fact that it shows as a warning despite being syncing normally is really annoying, it should clear that status on it’s own once syncing worked.
Those folders are special folders, and even though you cannot see them in windows explorer, if you were to try to create a folder with those names you get an error.
Regarless, Seafile should know about this and workaround this fact somehow.